The proposed project will test the internal and external validity of DSM-IV attention- deficit/hyperactivity disorder in an ethnically diverse population that includes a large proportion of African American and Hispanic children. Parent and teacher ratings of ADHD will be obtained for a large community sample of children in the Denver metropolitan area. The proposed study will provide the first estimates of the prevalence of DSM-IV ADHD among African American and Hispanic children, as well as the prevalence of each of the three diagnostic subtypes of DSM-IV ADHD. Several competing explanations for ethnic differences in the prevalence of ADHD will be tested, including rater bias and response to prejudice. Exploratory and confirmatory factor analysis will be used to test if the internal structure of the diagnosis varies as a function of ethnicity. Demographic variables such as socioeconomics status, location of residence, exposure to environmental stressors, and rater ethnicity will be assessed to test if these variables account for differences in the ratings of children from different ethnic groups. Measures of functional impairment and comorbid psychopathology will be administered to test if children with ADHD from different ethnic groups exhibit differences in these domains. In order to assess the etiology of ADHD in African American children, more extensive assessments will be conducted with 200 probands with ADHD and 200 comparison probands selected from the overall African American sample. Parental ADHD will be assessed to test if ADHD is significantly familial in an African American population, and data will be obtained regarding difficulties during pregnancy or delivery to test if perinatal complications are associated with ADHD. DNA samples will be obtained from all probands, their parents, and the biological sibling closest in age to the proband. Case- control and sib-pair comparisons, and the transmission disequilibrium test will be used to conduct the first for genetic association between several theoretically plausible candidates genes and ADHD in an AA sample.